214 
the abundance and character of these, it appears probable that 
this enlarged portion of the branch bore well-developed plants 
of mistletoe some years ago. Moreover it was seen, on stripping 
off the bark, that fairly numerous roots and sinkers of mistletoe, 
in a living condition, were present in this specimen, although 
there was such a poor external growth of the parasite. 
The conclusion derived from an examination of the specimens 
from Hampton Court is that, in these, enlargement of the branch 
is due to the presence of mistletoe. Further, the general 
supposition may be made that, where large swellings on branches 
of Lime bear mistletoe of meagre growth, vigorous plants of 
the parasite were present during the earlier stages of the 
enlargement, but that they may have since disappeared, perhaps 
having been torn off by the wind, after they had caused some 
cankering of the branch, and thereby loosened their hold. 
Though living roots, sinkers and buds of the parasite may be 
present in large swellings on the Lime, there would appear to be 
some condition usually inhibiting any strong aerial growth of 
mistletoe.. Possibly the thickness of the bark or the nature 
of the cork-layers of the Lime at this stage of the enlargement 
may be unfavourable to the development of the aerial stems of 
the mistletoe. 
n some parts of the specimens examined, the influence of 
the parasite in causing enlargement is clearly indicated. For 
instance, local enlargements were seen following the course of 
some roots and sinkers, which extended beyond the general 
limit of the swelling. Enlargement depends on increased breadth 
of the annual rings of the wood, and, to a small extent, on 
thickening of the bark. The influence of sinkers in inducing the 
formation of enlarged annual rings in the wood of the host was 
noted by Pitra,* and earlier by Schacht (quoted by Pitra). 
Pitra suggested by way of explanation that the streaming of 
sap towards the roots and sinkers of the mistletoe, due to the 
osmotic power of the latter, might cause an increased supply of 
nutritive material to be available for the adjacent cambial layer 
of the host. 
Some such cause may favour the rapid growth of wood in 
the neighbourhood of sinkers and roots during the earlier stages 
in the formation of the swelling, but there is another factor which 
perhaps may become important in the later stages. Owing to 
the disturbance of the cambial growth by sinkers and by the 
healing of canker-spots (opposite dead sinkers, etc.), the later 
formed wood and bast attain the type of structure found in 
burrs,f the grain running in various directions at different points. 
The presumable effect of this confused and often intricate course 
of the conducting elements would be a slow longitudinal trans- 
ference of sap, and consequent congestion of food materials, 
in the swollen region, locally increased cambial growth being 
* Pitra, Bot. Zeitung, vol. 19 (1861), p. 64. 
Tt This was clearly seen in the large specimen from Hampton Court. 
